1. Field of the Invention
The present invention relates to a temperature control method for a semiconductor manufacturing apparatus, etc., and particularly to a temperature control method of controlling the temperature of a treatment target according to a target temperature by using as a heating unit as a heater which is divided into plural heating zones.
2. Description of the Related Art
A vertical type furnace has been practically used as a batch type thermal treatment apparatus for performing a thermal treatment such as oxidation, diffusion, CVD, etc. on many semiconductor wafers from the viewpoint that suction of air into a reaction tube during a wafer input or takeout operation is little and thus the growth of natural oxidation film can be suppressed.
The batch type thermal treatment apparatus such as the vertical type furnace or the like has been used while segmentalized into various thermal treatment steps in accordance with the type of each thermal treatment, the type of film, the electrical characteristic expected to the film type or the like. In each of the segmentalized thermal steps, the temperature, the gas flow rate, the pressure, etc. which are strictly set in connection with each step so that a thermally-treated semiconductor wafer has an expected performance. Accordingly, from the viewpoint of the temperature control function, the thermal treatment apparatus has been required as one of important functions that uniform and high-precision temperature control is performed on all treatment targets in the thermal treatment process while the temperature which is set to various values is set as a target temperature.
From this point of view, the temperature control is required in the thermal treatment furnace so that the temperature of the treatment target in the thermal treatment process is coincident with a given target temperature to the utmost extent.
The existing vertical type thermal treatment furnace will be described hereunder with reference to FIG. 5. FIG. 5 is a longitudinally-sectional view showing the construction of the thermal treatment furnace 1.
The thermal treatment furnace 1 has a cylindrical heater 2, and supported by a heater base 3 so as to be vertically disposed. A reaction tube 4 and an inner tube 5 are disposed inside the heater 2 so as to be concentric with the heater 2. The reaction tube 4 is formed of quartz, for example, and designed in such a cylindrical shape that the inner diameter thereof is larger than the outer diameter of the inner tube 5, the upper end thereof is closed and the lower end thereof is opened. The inner tube 5 is formed of quartz, for example, and designed in such a cylindrical shape that the upper and lower ends thereof are opened. The inner tube 5 is disposed inside the reaction tube 4, and semiconductor wafers (hereinafter referred to as “treatment substrates”) as thermal treatment targets are accommodated in the cylindrical hollow portion of the inner tube 5 under the state that the treatment substrates are arranged in a horizontal position in a multistage style in the vertical direction by a boat 11.
A cylindrical flange 6 is concentrically disposed at the lower side of the reaction tube 4 so as to support the reaction tube 4 and the inner tube 5. Furthermore, an exhaust pipe 7 is mounted on the cylindrical flange 6 and intercommunicates with the lower end portion of a cylindrical space formed by the gap between the reaction tube 4 and the inner tube 5 so that gas in the reaction tube 4 can be discharged.
A cap 8 is provided below,the cylindrical flange 6 so that the opening portion at the lower end of the cylindrical flange 6 is hermetically closed by the cap 8. The cap 8 is connected to an elevator (not shown). When the elevator moves downwardly, the boat 11 and the spacer 12 can be carried out from the inner tube 5, and when the elevator moves upwardly, the boat 11 and the spacer 12 can be carried into the inner tube 5. A hermetically sealed thermal treatment area 9 is formed by the reaction tube 4, the cylindrical flange 6 and the cap 8.
A gas introducing nozzle 10 is connected to the cap 8 so as to intercommunicate with the thermal treatment area 9, and introduces reaction gas into the thermal treatment area 9 according to a gas flow rate controller (not shown). The boat 11 is formed of quartz, for example, and keeps the treatment substrates in a horizontal position and in a tandem and multistage arrangement while the centers of the treatment substrates are aligned with one another. The boat 11 is mounted and supported on the cap 8 through a spacer 12.
In order to perform the temperature control on the heat treatment area 9 with higher precision, the heater 2 is divided into plural heating zones. In the case of FIG. 5, the heater 2 is divided into three zones. When it is necessary to individually show the heater 2 every zone, the heater 2 is represented by 20a, 20b and 20c in connection with the respective zones. Areas of the thermal treatment area 9 which are affected by the heat of the divided heaters are represented by a zone, b zone and c zone in connection with the heaters 20a, 20b, 20c as occasion demands. Power supply units 13a, 13b, 13c (represented as a power supply unit 13 when generically named) are connected to the heater 2. The power supply unit 13 supplies predetermined power to the heater 2 on the basis of an instruction value output from a temperature controller 14 described later.
In-furnace temperature sensors 21a, 21b, 21c (represented as an in-furnace temperature sensor 21 when named generically) are provided in the gap between the reaction tube 4 and the heater 2 so as to correspond to the heating zones, and the temperature in the reaction tube 4 is detected by these sensors (also called as the temperature of the a zone, the temperature of the b zone and the temperature of the c zone). The temperature controller 14 contains a control algorithm for making the detection temperature of the in-furnace temperature sensor 21 approach to a desired value, and it executes the control calculation on the basis of these data and outputs the calculation result to the power supply unit 13.
Next, a method of forming thin film on a treatment substrate with a CVD method as one style of the thermal treatment by using the thus-constructed thermal treatment furnace 1 will be described.
When plural treatment substrates are loaded into the boat 11 under the state that the boat 11 and the spacer 12 are located out of the thermal treatment area 9, the boat 11 is carried into the thermal treatment area 9 through the cap 8 and the spacer 12 by upward motion of the elevator (not shown).
Subsequently, the thermal treatment area 9 is heated by the heater 2 so as to be equal to a desired temperature. At this time, a target temperature is first set in the temperature controller 14. The temperature controller 14 carries out the control calculation on the basis of the detection temperature of the in-furnace temperature sensor 21 and the target temperature and outputs the calculation result to the power supply unit 13. The power supply unit 13 supplies current to the heater 2 so as to generate indicated heat. The detection of the temperature by the in-furnace temperature sensors 21, the control calculation of the temperature controller 14 and the heating current supply of the power supply unit 13 are repeated at a sufficiently short period, whereby the thermal treatment area 9 is temperature-controlled to be equal to the target temperature.
Subsequently, gas whose flow rate is controlled to a desired flow rate is introduced from a gas introducing nozzle 10 into the thermal treatment area 9. The introduced gas moves upwardly inside the inner tube 5, flows out from the opening at the upper end of the inner tube 5 into the cylindrical gap formed by the gap between the reaction tube 4 and the inner tube 5, and then discharged from the exhaust pipe 7. The gas comes into contact with the treatment substrates while passing through the thermal treatment area 9, and at this time thin film is formed on the treatment substrates by the CVD reaction.
When a preset treatment time elapses, the gas in the thermal treatment area 9 is replaced by inert gas, and also the temperature of the thermal treatment area 9 is reduced to such a sufficiently low temperature that the treatment substrates can be carried out. Thereafter, the boat 11 is carried out from the thermal treatment area 9 by downward motion of the elevator (not shown).
A thermocouple is normally used as the in-furnace temperature sensor 21. Therefore, in order to prevent metal pollution to the treatment substrates and occurrence of particles, the in-furnace temperature sensor 21 is disposed at the outside of the reaction tube 4 as shown in FIG. 5. Therefore, the in-furnace temperature sensor 21 cannot directly detect the temperature of the treatment substrates in the thermal treatment area 9. Therefore, this technique provides such a temperature system that the temperature of the treatment substrates in the thermal treatment area 9 is expected to be equal to a desired value by controlling the detection temperature of the in-furnace temperature sensor 21. However, there is an error between the temperature of the treatment substrates and the detection temperature of the in-furnace temperature sensor 21 when the thermal treatment is actually carried out. Accordingly, the thermal treatment is actually carried out at a temperature different from the target temperature with high probability, and thus the quality of the thermal treatment is lowered.
Under the background as described above, in order to perform temperature control of making the temperature of the treatment substrates approach to the target temperature as closely as possible, it may be considered that the temperature sensor is closer to the treatment substrates to perform the temperature control.
FIG. 6 shows a thermal furnace 1 in which a new temperature detecting unit (profile temperature sensor 15) is added to detect a temperature which is closer to the temperature of the treatment substrates than the detection temperature of the in-furnace temperature sensor 21. The profile temperature sensor 15 penetrates through the cap 8 and is disposed inside the inner tube 5 to detect the temperature closer to the treatment substrates. In order to implement the temperature control in the thermal treatment area 9 on the basis of the profile temperature sensor 15, the profile temperature sensor 15 is provided with detection points (sensors) whose number is equal to the division number of the heater, and the detection points (heaters) of the profile temperature sensor 15 are normally disposed at the same positions of the detection points of the in-furnace temperature sensor 21 in the long axis direction. In the example of FIG. 6, three detection points (sensors) (represented by 15a, 15b, 15c when they are individually handled), and the detected temperatures thereof are input to the temperature controller 14. The temperature controller 14 performs the temperature control so that the detection temperature of the profile temperature sensor 15 approaches the target temperature.
FIG. 7 is a diagram showing the position relationship of the heater 2, the in-furnace temperature sensor 21 and the profile temperature sensor 15 by extracting these elements from FIG. 6, and also shows an example of a temperature distribution in the long-axis direction in the thermal treatment area 9.
In FIG. 7, Ta, Tb, Tc represent the detection temperatures of the profile temperature sensors 15a, 15b, 15c. The detection temperatures of the profile temperature sensors 15 are substantially coincident with target temperature Y if the control algorithm of the temperature controller 14 is proper.
In the example of FIG. 7, the temperature at the intermediate position between Ta and Tb or the temperature at the intermediate position between Tb and Tc does not reach the target temperature Y. In this case, there is a case where in order to make the overall thermal treatment area 9 uniformly approach the target temperature, it is better not to make Ta, Tb, Tc approach the target temperature Y, but to make Ta, Tb, Tc approach temperature which is slightly higher than the target temperature. However, conversely to this case, there is a case where the temperature at the intermediate point exceeds the target temperature, and thus the above countermeasure is insufficient.
Therefore, a thermal treatment furnace 1 as shown in FIG. 1 may be used to grasp the temperature distribution in more detail in place of the provision of the profile temperature sensors 15 whose number is equal to the division number of the heater 2.
In FIG. 1, in order to detect the temperature distribution in the thermal treatment area 9 in detail, the profile temperature sensor 15 is provided with detection points (sensors) whose number exceed the division number of the heater, and arranged so as to cover the area where the treatment substrates exist. In the example of FIG. 1, eight sensors (represented like a profile temperature sensor 15-1 if it is necessary to individually represent each profile temperature sensor), and the detected temperature is input to the temperature controller 14.
Japanese patent No. 3834216 discloses, as a technique related to the present invention, a temperature control method which controls a heating device having at least two heating zones so that the detection temperature is set to target temperature at a predetermined position and in which temperature is detected at positions whose number is larger than the number of heating zones so that temperature at one predetermined position is detected in each heating zone and the heating device is controlled so that the difference between the target temperature and the detection temperatures at the plural predetermined positions is reduced. According to this patent, the correlation between a cascade thermocouple corresponding to the in-furnace temperature sensor 21 of the above invention and a well having a thermocouple or a profile thermocouple corresponding to the profile temperature sensor of the above invention is determined in advance, and the cascade thermocouple is controlled on the basis of the determined correlation so as to achieve the target temperature.
In the above technique, temperature is detected at many detection points (predetermined positions). However, when the temperature control is performed, one point of the profile temperature sensors 15 set at the respective detection points is selected for each zone (or the in-furnace temperature sensor 3) and the detection temperature thereof is controlled.
This will be described in detail with reference to FIG. 2. FIG. 2 is a diagram showing the positional relationship of the heater 2, the in-furnace temperature sensor 21 and the profile temperature sensor 15 which is clarified by extracting these elements from FIG. 1, and the detection points of the profile temperature sensor 15 are clarified by using 15-1 to 15-8. In FIG. 2, the control is performed in the related technique by adopting the detection temperature of the profile temperature sensor 15-1 located at the position nearest to the in-furnace temperature sensor 21a, the detection temperature of the profile temperature sensor 15-5 located at the position nearest to the in-furnace temperature sensor 21b and the detection temperature of the profile sensor 15-7 nearest to the in-furnace temperature sensor 21c out of the eight profile temperature sensors 15 in place of the detection temperature of the in-furnace temperature sensor 21a, the detection temperature of the in-furnace temperature sensor 21b and the detection temperature of the in-furnace temperature sensor 21c, respectively.